The use of heat-activated binder fibers in carpet yarns to improve retention of tuft identity, resulting in increased wear resistance and carpet life, is disclosed in the published patent applications Hackler, PCT-WO 88/03969 and Watt & Fowler GB 2205116-A. The referenced published applications teach that bulked continuous filament (BCF) yarns containing low-melting binder filament yarns may be produced using conventional manufacturing methods but do not disclose or give examples as to where in the process or how the binder filament is incorporated into and intermingled with the base continuous filament yarn.
Methods suggested by the prior art have various shortcomings. The binder and BCF yarns may be ply-twisted together in the carpet mill prior to tufting; however this will lead to binding of individual plies rather than binding the filaments within each tuft. An additional disadvantage of using this method is that the fiber producer is unable to ensure the quality of tuft bonding in the final carpet since the process for incorporating the binder filaments in the yarn is carried out in the carpet mill. A further drawback of this method is that when the binder filaments are twisted together with the BCF yarn, the binder filaments are essentially wrapped around the outside of the BCF yarn bundle. When these yarns are heatset with moist heat as in a Superba heat-setting apparatus (where typically 6-24 twisted ends are heat-set simultaneously on a moving belt) or in an autoclave (where yarn skeins are used), the ends may stick together to an unacceptable degree. Such sticking can be a particular problem for a Superba process as the line has to be shut down whenever the bundles are stuck together.
The binder filaments may also be added prior to drawing the base continuous yarn and the two yarns co-bulked and interlaced in a process similar to that disclosed in De Howitt, U.S. Pat. No. 4,612,150. However, in this case the binder fiber melts on the hot rolls, and the process becomes inoperable. Although the temperature of the hot rolls may be reduced to avoid melting of the binder fiber, in such event inadequate carpet bulk is obtained.
Another option is to add the binder fiber after the heated draw rolls but before the bulking/interlacing jet. However, residual heat in the base fiber coming off the heated draw rolls and the heat in the bulking fluid used in the jet may be sufficient to soften and melt the binder fiber and cause it to break intermittently along the length of the base continuous filament yarn. The broken filaments cause severe housekeeping problems in the areas of both the BCF machine and the twisting equipment. Again, the bulking temperature may be reduced to eliminate breaks, but this tends to result in insufficient bulk. Yet another option is to add the binder fibers to the continuous filament yarn after it passes through the bulking/interlacing jet. However, since the BCF yarn is well-interlaced at this point, it is not possible to achieve optimum intermingling of the BCF and binder filaments. This results in filament breaks in downstream mill operations such as twisting, knit-de-knit processing, or tufting.
The process of the current invention overcomes the above-mentioned problems by incorporating binder fibers into a base continuous filament yarn in a manner which maximizes the bulk and degree of intermingling of the two components and eliminates filament breaks in the low-melting component. A further advantage of the present invention is that the process may be run at high speeds, in excess of 2000 yd/minute (1829 m/minute) with excellent bulk and interlace in the final two-component yarn.